Lithium manganese iron phosphate positive pole slurry and preparation method thereof, positive pole piece and preparation method thereof, and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and provides a lithium iron manganese phosphate positive electrode slurry and a preparation method thereof, a positive electrode plate and a preparation method thereof, and a lithium ion battery, a conductive adhesive liquid is prepared, the conductive adhesive liquid contains a binder, a dispersant, carbon nanotubes and a solvent, and the binder is polyvinylidene fluoride; dividing the conductive agent glue solution into two parts P1 and P2; mixing the P1 with an active material to obtain first slurry; and P2 is mixed with the first slurry to obtain the positive electrode slurry, the amount of the binder in the P1 is M1, the amount of the binder in the P2 is M2, and in percentage by mass, M1 / (M1 + M2) is equal to 40%-80%; the active material contains lithium manganese iron phosphate and conductive carbon black. According to the lithium manganese iron phosphate positive electrode slurry, the positive electrode plate, the preparation method of the positive electrode plate and the lithium ion battery provided by the invention, the problems of easy agglomeration, difficult dispersion and the like caused by small particle size and the problems of large glue absorption amount, slurry sedimentation, coating powder falling, low binding power and the like caused by large specific surface area can be solved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and particularly to lithium manganese iron phosphate cathode slurry and its preparation method, cathode sheet and its preparation method, and lithium-ion battery. Background Technology

[0002] Lithium manganese iron phosphate (LMFP) has a higher voltage platform than lithium iron phosphate (LFP) and about 15% higher energy for the same capacity, making it more competitive. However, due to manganese doping, LMFP has poor electronic and ionic conductivity and poor electrochemical performance. Therefore, in commercial applications, LMFP is usually modified by carbon coating, nano-sizing, and doping.

[0003] Slurry preparation is a crucial step in lithium-ion battery manufacturing, accounting for 30% of the process and playing a decisive role. The quality of the slurry directly impacts the coating and the overall performance of the final lithium-ion battery. In actual production, nano-sizing techniques can effectively enhance the conductivity of LMFPs, with primary particles typically having an average particle size of 20–300 nm and a specific surface area of ​​approximately 15–30 m² / g. However, during slurry preparation, on the one hand, small-diameter LMFP particles are prone to agglomeration, leading to difficulties in sieving the slurry, coating particles, and scratches. On the other hand, the small-diameter, large-specific-surface-area LMFP absorbs a large amount of adhesive, reducing the adhesion between active particles and between active particles and the foil. This ultimately results in problems such as electrode coating powder shedding, cracking, and powder shedding during rolling, severely affecting the electrical and safety performance of LMFP lithium-ion batteries.

[0004] Current homogenization techniques improve processing performance by combining small-particle LMFP with other large-particle materials (such as ternary materials), but they do not fundamentally address the inherent processing problems of LMFP material itself, such as dispersion difficulties caused by its small particle size and large specific surface area. Therefore, there is an urgent need to develop a method that can solve the dispersion difficulties encountered during the homogenization of small-particle-size, large-specific-surface-area LMFP, while also improving the slurry's adhesion and stability, and improving the bonding effect of LMFP electrodes as well as addressing issues such as electrode cracking, powder shedding, and particle scratches. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a lithium manganese iron phosphate cathode slurry and its preparation method, a cathode electrode and its preparation method, and a lithium-ion battery. By employing a semi-dry homogenization process and controlling the binder content, the invention effectively improves the problems of small particle agglomeration, poor slurry stability, coating particle scratches, cracking, and powder shedding that occur in the existing lithium manganese iron phosphate production process, thereby producing a lithium-ion battery with excellent overall performance.

[0006] In a first aspect, the present invention provides a method for preparing a lithium manganese iron phosphate cathode slurry, comprising preparing a conductive adhesive liquid, wherein the conductive adhesive liquid contains a binder, a dispersant, carbon nanotubes and a solvent, wherein the binder is polyvinylidene fluoride; dividing the conductive adhesive liquid into two parts, P1 and P2; mixing P1 with an active material to obtain a first slurry; mixing P2 with the first slurry to obtain the cathode slurry; wherein the amount of binder in P1 is M1 and the amount of binder in P2 is M2, and by mass percentage, M1 / (M1+M2) = 40% to 80%; wherein the active material contains lithium manganese iron phosphate and conductive carbon black.

[0007] As a preferred embodiment, based on 100wt% of the active material, the amount of lithium manganese iron phosphate is 95wt% to 98wt%, and the amount of conductive carbon black is 0.4wt% to 1wt%.

[0008] In a preferred embodiment, the solid content of the first slurry is 65wt% to 75wt%.

[0009] In a preferred embodiment, the polyvinylidene fluoride has a molecular weight of 700,000 to 1,200,000 (weight-average molecular weight).

[0010] In a preferred embodiment, the binder accounts for 5% to 8% of the solvent by mass.

[0011] As a preferred embodiment, based on 100wt% of the conductive agent solution, the amount of binder is 1.8wt% to 2.8wt%, the amount of dispersant is 0.2wt% to 0.6wt%, and the amount of carbon nanotubes is 0.2wt% to 1wt%.

[0012] In a preferred embodiment, the solvent is N-methylpyrrolidone.

[0013] In a preferred embodiment, the adhesive is one or more of HSV900, 5130, and 6020.

[0014] In a preferred embodiment, the carbon nanotubes are one or more of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes. Preferably, they are first prepared with NMP to obtain a carbon nanotube slurry with a solid content of 4 wt% to 6 wt%.

[0015] In a preferred embodiment, the dispersant is one or more of polyvinylpyrrolidone, sodium dodecyl sulfate, fatty alcohol polyoxyethylene ether, Tween-60, and dispersant KD-1.

[0016] In a preferred embodiment, the method further includes a post-processing step, which includes viscosity adjustment, defoaming, and sieving; when the viscosity of the positive electrode slurry is 5000-7000 mPa•s, defoaming and sieving are performed; when the viscosity of the positive electrode slurry is >7000 mPa•s, solvent is added to adjust the viscosity to 5000-7000 mPa•s, and then defoaming and sieving are performed.

[0017] Secondly, the present invention provides lithium manganese iron phosphate cathode slurry prepared by any of the above methods.

[0018] In a preferred embodiment, the positive electrode slurry contains solid components, which include lithium manganese iron phosphate, conductive carbon black, carbon nanotubes, binder, and dispersant, with mass fractions of 95%–98%, 0.4%–1%, 0.2%–1%, 1.8%–2.8%, and 0.2%–0.6%, respectively.

[0019] Preferably, the viscosity of the lithium manganese iron phosphate cathode slurry is 5000-7000 mPa•s.

[0020] Preferably, the fineness of the lithium manganese iron phosphate cathode slurry is 3–30 μm.

[0021] Preferably, the solid content of the lithium manganese iron phosphate cathode slurry is 50wt% to 65wt%.

[0022] Thirdly, the present invention provides a lithium manganese iron phosphate cathode sheet containing lithium manganese iron phosphate cathode slurry prepared by any of the methods described in the first aspect or containing any of the lithium manganese iron phosphate cathode slurries described in the second aspect.

[0023] Fourthly, the present invention provides a method for preparing the lithium manganese iron phosphate positive electrode sheet as described in the third aspect, wherein the lithium manganese iron phosphate positive electrode slurry is coated on a carbon-coated aluminum foil, and the single-sided density is 17~23 mg / cm³. 2， The coating speed is 5–10 m / s, the coating temperature is 84–93℃, and the compaction density is 2.0–2.5 g / cm³. 3 After being rolled and slit, lithium manganese iron phosphate positive electrode sheets are obtained.

[0024] Fifthly, the present invention provides a lithium-ion battery comprising the lithium manganese iron phosphate positive electrode sheet described in the third aspect.

[0025] The lithium manganese iron phosphate cathode slurry, cathode sheet, preparation method, and lithium-ion battery provided by this invention can solve the problems of easy agglomeration and difficulty in dispersion caused by small particle size, and the problems of large adhesive absorption, slurry sedimentation, coating powdering, and low adhesion caused by large specific surface area.

[0026] The wet two-step adhesive addition process proposed in this invention can shorten the homogenization time, enable continuous and automated production, and control the content of binder to avoid the agglomeration of nano LMFP particles that leads to slurry gelation, as well as the sedimentation of LMFP particles due to insufficient adhesion. This ensures that the slurry has a high solids content and high areal density, while also taking into account the adhesion and flexibility of the electrode sheet, and improving the coating cracking and powdering phenomena. Attached Figure Description

[0027] Figure 1 This refers to the solid content of the LMFT cathode slurry.

[0028] Figure 2 The fineness of the LMFT cathode slurry.

[0029] Figure 3 This is the viscosity of the LMFT cathode slurry.

[0030] Figure 4 This is the LMFT positive electrode film resistor.

[0031] Figure 5 The LMFT is the peeling force of the positive electrode sheet.

[0032] Figure 6-1 This is the kneading situation in Example 1.

[0033] Figure 6-2 For comparison example 6, the kneading situation is shown.

[0034] Figure 7-1 This is the coating situation for Example 1.

[0035] Figure 7-2 Comparative Example 1: Coating conditions.

[0036] Figure 7-3 This is for the coating situation of Comparative Example 5.

[0037] Figure 8-1 This is the folded state of the roller-pressed electrode sheet in Example 1.

[0038] Figure 8-2 The image shows the folded state of the two roller-pressed electrode sheets as a comparative example.

[0039] Figure 8-3 The image shows the folded state of the 4-roller electrode sheet as a comparative example. Detailed Implementation

[0040] The present invention will be further described below with reference to specific embodiments, but this does not constitute any limitation on the present invention.

[0041] The lithium manganese iron phosphate cathode slurry, cathode sheet, and their preparation methods, as well as the preparation method of lithium-ion batteries, include the following steps.

[0042] (1) Preparation of adhesive solution: The adhesive and solvent are mixed evenly to prepare the adhesive solution. The adhesive is polyvinylidene fluoride with a molecular weight of 700,000 to 1,200,000. The adhesive accounts for 5% to 8% of the mass fraction of the adhesive solution.

[0043] (2) Preparation of conductive agent adhesive: The dispersant and carbon nanotube slurry are mixed evenly with the binder adhesive to prepare the conductive agent adhesive, wherein the dispersant, carbon nanotube and binder account for 6% to 10% of the mass fraction of the conductive agent adhesive.

[0044] (3) Active mixture: Lithium manganese iron phosphate and conductive carbon black are mixed evenly to obtain active powder.

[0045] (4) First addition of binder: The conductive agent solution prepared in step (2) is added to the active powder prepared in step (3). The mass of binder in the conductive agent solution added in step (4) is 40% to 80% of the total mass of binder required for the lithium manganese iron phosphate cathode slurry. Solvent is added and mixed evenly to prepare a first slurry with a solid content of 65wt% to 75wt%.

[0046] (5) Secondary addition of adhesive: The conductive agent solution prepared in step (2) is added to the first slurry prepared in step (4). The total mass of the binder in the binder solution added in steps (4) and (5) is equal to the total mass of the binder required for the lithium manganese iron phosphate cathode slurry. The mixture is mixed evenly to prepare a second slurry with a viscosity of 5000 to 12000 mPa•s.

[0047] (6) Post-processing: If the viscosity of the second slurry prepared in step (5) is 5000-7000 mPa•s, the second slurry is defoamed and sieved to obtain the lithium manganese iron phosphate cathode slurry; if the viscosity of the second slurry prepared in step (5) is >7000 mPa•s, a solvent is added to the second slurry prepared in step (5) to adjust the viscosity to 5000-7000 mPa•s. After adjusting the viscosity, the slurry is defoamed and sieved to obtain the lithium manganese iron phosphate cathode slurry.

[0048] (7) Coating and Rolling: The lithium manganese iron phosphate cathode slurry obtained in step (6) is coated onto carbon-coated aluminum foil, with a single-sided density of 17.53 mg / cm³. 2 The coating speed is 8 m / min, the coating temperature is 84~93℃, and the compaction density is 2.3 g / m³. 3 After being rolled and slit, the LMFP positive electrode sheet is obtained.

[0049] (8) Preparation of lithium-ion battery: The obtained positive electrode sheet is used as the positive electrode, electrolyte, negative electrode and separator of lithium-ion battery to prepare lithium-ion battery.

[0050] The materials used in the embodiments and comparative examples of this invention are described below.

[0051] Polyvinylidene fluoride, PVDF, HSV900.

[0052] N-methylpyrrolidone, NMP.

[0053] Lithium manganese iron phosphate, LMFP.

[0054] Example 1 The method for preparing lithium manganese iron phosphate cathode slurry, cathode sheet and lithium-ion battery includes the following steps.

[0055] Step (1) Preparation of adhesive solution: Add PVDF adhesive and NMP solvent to a mixing tank at a mass ratio of 1:13.3, and pre-stir at a stirring speed of 2.7 m / s for 25±2℃ for 30 min (pre-stirring is to prevent PVDF from flying away and being drawn away during high-speed dispersion under vacuum, which would reduce the actual solid content); then disperse at a stirring speed of 18.7 m / s, a temperature controlled at 35~45℃, and a vacuum degree of ≤-90kPa for 150 min to prepare the adhesive solution.

[0056] Step (2) Preparation of conductive agent solution: The dispersant polyvinylpyrrolidone (PVP), carbon nanotube slurry (Cabot GNC-N-19) and the binder solution prepared in step (1) are added to a mixing tank at a mass ratio of 1:12.5:89.3. The mixture is dispersed for 60 min at a temperature of 35~45℃ and a vacuum degree of ≤-90kPa with a stirring linear speed of 13.4m / s to prepare the conductive agent solution.

[0057] Step (3) Activation mixing: The positive electrode active material LMFP and conductive carbon black (the mass ratio of LMFP to conductive carbon black is 96.3:0.55) are simultaneously added to the mixing tank for dry mixing. The linear velocity is controlled at 2.7m / s, the temperature is 25±2℃, and the stirring time is 30min to obtain the active powder.

[0058] Step (4) First addition of adhesive: The conductive agent solution prepared in step (2) is added to the powder prepared in step (3). The mixing ratio is LMFP to PVDF, carbon nanotubes and dispersant at a mass ratio of 96.3:1.25:0.125:0.2. Then, solvent NMP is added at a mass ratio of NMP:LMFP=0.22:1. The mixture is stirred at a linear speed of 0.5 m / s, at a temperature of 25±2℃ and a kneading time of 120 min to prepare a first slurry with a solid content of 72 wt%. The mass of PVDF in the first slurry accounts for 50% of the total mass of PVDF contained in the positive electrode slurry.

[0059] Step (5) Secondary sizing: The conductive agent solution prepared in step (2) is added to the first slurry prepared in step (4). The mixing ratio is LMFP to PVDF, carbon nanotubes and dispersant in a mass ratio of 96.3:2.5:0.25:0.4. Then, solvent NMP is added with a mass ratio of NMP:LMFP=0.13:1. The mixture is pre-dispersed for 20 min at a stirring speed of 6.8 m / s, a temperature of 30~40℃ and a vacuum degree of ≤-90 kPa. Then, it is high-speed dispersed for 120 min at a stirring speed of 17.7 m / s, a temperature controlled at 30~40℃ and a vacuum degree of ≤-90 kPa to prepare a second slurry with a solid content of 58 wt%, a viscosity between 5000 and 12000 mPa·s and exhibiting a fluid dynamic state.

[0060] Step (6) Viscosity Adjustment: Add an appropriate amount of NMP solvent to adjust the viscosity of the second slurry (each addition is made at a mass ratio of NMP:LMFP = 0.025 until the slurry viscosity is controlled within the range of 5000–7000 mPa·s). Control the stirring speed at 6.8 m / s, the adjustment time at 30 min, the temperature at 25 ± 2℃, and the vacuum degree at ≤-90 kPa. Adjust the slurry viscosity to 7000 mPa·s. After defoaming, pass the slurry through a 150-mesh sieve to obtain the lithium manganese iron phosphate cathode slurry. The mass ratio of LMFP, conductive carbon black, carbon nanotubes, PVDF, and dispersant in the prepared lithium manganese iron phosphate cathode slurry is 96.3:0.55:0.25:2.5:0.4.

[0061] Step (7) Coating and Rolling: The lithium manganese iron phosphate cathode slurry obtained in step (6) is coated onto carbon-coated aluminum foil, with a single-sided density of 17.53 mg / cm³. 2 The coating speed is 8 m / min, the coating temperature is 84–93℃, and after rolling, the electrode compaction density is 2.3 g / m³. 3 After slitting, the LMFP positive electrode sheet is obtained.

[0062] Step (8) Preparation of lithium-ion battery: The positive electrode sheet prepared above is used as the positive electrode of lithium-ion battery, and assembled with electrolyte, negative electrode and separator to obtain lithium-ion battery.

[0063] Electrolyte: 1 mol LiPF6 EC:EMC:DEC (3:4:3).

[0064] Negative electrode material: Negative electrode sheets are made from commercial graphite.

[0065] Membrane material: PP membrane.

[0066] A 5Ah soft-pack lithium-ion battery is produced through processes such as winding, hot pressing, packaging, baking, liquid injection, formation, degassing, and capacity testing.

[0067] Example 2 The lithium manganese iron phosphate cathode slurry, cathode electrode and lithium-ion battery were prepared according to the method of Example 1, with the only difference being that in step (4), the mixing ratio was 96.3:1.75:0.175:0.28, that is, the mass of PVDF in the first slurry accounted for 70% of the total mass of PVDF contained in the cathode slurry, and a first slurry with a solid content of 72wt% was prepared.

[0068] In Example 2, the mass ratio of LMFP, conductive carbon black, carbon nanotubes, PVDF and dispersant in the lithium manganese iron phosphate cathode slurry was 96.3:0.55:0.25:2.5:0.4.

[0069] Comparative Example 1 The method for preparing lithium manganese iron phosphate cathode slurry, cathode sheet, and lithium-ion battery using a dry homogenization process is as follows.

[0070] (1) Mixing: The positive electrode active material LMFP, conductive carbon black and binder PVDF in a mass ratio of 96.3:0.55:2.5 are simultaneously added to a mixing tank for dry mixing. The linear velocity is controlled at 2.7m / s, the mixing time is 30min, and the temperature is 25±2℃ to obtain dry mixed powder.

[0071] (2) Kneading: Add solvent NMP (NMP:LMFP=0.36:1) to the powder obtained in step (1), control the stirring linear speed to be 0.5m / s, kneading time to be 120min, 25±2℃, and prepare the first slurry with a solid content of 72wt%.

[0072] (3) Preparation of conductive agent slurry: Carbon nanotube slurry (Cabot GNC-N-19) is added to the first slurry obtained in step (2). The mixing ratio is 96.3:0.25 by mass of LMFP to carbon nanotube. The stirring linear speed is controlled at 0.5 m / s, the temperature is controlled at 30~40℃, and the vacuum degree is ≤-90kPa. The slurry is stirred for 30 min to prepare the conductive agent slurry.

[0073] (4) Add dispersant: Add polyvinylpyrrolidone (PVP) dispersant to the conductive agent slurry obtained in step (3). The mixing ratio is 96.3:0.4 by mass of LMFP to dispersant. The mixture is dispersed at high speed for 120 min under the conditions of stirring linear speed of 17.7 m / s, temperature control of 30~40℃ and vacuum degree of ≤-90kPa to prepare a second slurry with viscosity between 5000 and 12000 mPa·s and exhibiting a fluid dynamic state.

[0074] (5) Viscosity adjustment: Add an appropriate amount of solvent NMP according to the viscosity of the second slurry to adjust the viscosity. Control the stirring linear speed to 6.8m / s, the viscosity adjustment time to 30min, the temperature to 25±2℃, the vacuum degree to ≤-90kPa, and adjust the slurry viscosity to 7000mPa·s. After defoaming, pass through a 150-mesh sieve to obtain the lithium manganese iron phosphate cathode slurry.

[0075] In Comparative Example 1, the mass ratio of LMFP, conductive carbon black, carbon nanotubes, PVDF and dispersant in the lithium manganese iron phosphate cathode slurry was 96.3:0.55:0.25:2.5:0.4.

[0076] (6) Coating and Rolling: The lithium manganese iron phosphate cathode slurry obtained in step (5) is coated onto carbon-coated aluminum foil, with a single-sided density of 17.53 mg / cm³. 2 The coating speed is 8 m / min, the coating temperature is 84~93℃, and the compaction density is 2.3 g / m³. 3 After being rolled and slit, the LMFP positive electrode sheet is obtained.

[0077] The LMFP positive electrode sheet prepared above was used as the positive electrode of the lithium-ion battery, and the lithium-ion battery was prepared according to step (8) of Example 1.

[0078] Comparative Example 2 The preparation of lithium manganese iron phosphate cathode slurry, cathode sheet, and lithium-ion battery includes the following steps.

[0079] Step (1) Preparation of adhesive solution: Add PVDF adhesive and NMP solvent to a mixing tank at a mass ratio of 1:13.3, and pre-stir at a stirring speed of 2.7 m / s for 25±2℃ for 30 min (pre-stirring is to prevent PVDF from flying away and being drawn away during high-speed dispersion under vacuum, which would reduce the actual solid content); then disperse at a stirring speed of 18.7 m / s, a temperature controlled at 35~45℃, and a vacuum degree of ≤-90kPa for 150 min to prepare the adhesive solution.

[0080] Step (2) Preparation of conductive agent solution: The dispersant polyvinylpyrrolidone (PVP), carbon nanotube slurry (Cabot GNC-N-19) and the binder solution prepared in step (1) are added to a mixing tank at a mass ratio of 1:12.5:89.3. The mixture is dispersed for 60 min at a temperature of 35~45℃ and a vacuum degree of ≤-90kPa with a stirring linear speed of 13.4m / s to prepare the conductive agent solution.

[0081] Step (3) Activation mixing: The positive electrode active material LMFP and conductive carbon black (the mass ratio of LMFP to conductive carbon black is 96.3:0.55) are simultaneously added to the mixing tank for dry mixing. The linear velocity is controlled at 2.7m / s, the temperature is 25±2℃, and the stirring time is 30min to obtain the active powder.

[0082] Step (4) First addition of adhesive: The conductive agent solution prepared in step (2) is added to the powder prepared in step (3). The mixing ratio is LMFP to PVDF, carbon nanotubes and dispersant at a mass ratio of 96.3:0.55:0.25:2.5:0.4. Then, solvent NMP is added at a mass ratio of NMP:LMFP=0.01:1. The mixture is stirred at a linear speed of 0.5 m / s, at a temperature of 25±2℃ and a kneading time of 120 min to prepare a first slurry with a solid content of 72 wt%. The mass of PVDF in the first slurry accounts for 100% of the total mass of PVDF contained in the positive electrode slurry.

[0083] Step (5) Add solvent: Add solvent NMP to the first slurry at a mass ratio of NMP:LMFP=0.35:1. Pre-disperse for 20 min at a stirring speed of 6.8 m / s, a temperature of 30~40℃, and a vacuum degree of ≤-90 kPa. Then, disperse at high speed for 120 min at a stirring speed of 17.7 m / s, a temperature of 30~40℃, and a vacuum degree of ≤-90 kPa to prepare a second slurry with a solid content of 58 wt%, a viscosity between 5000 and 12000 mPa·s, and exhibiting a fluid dynamic state.

[0084] Step (6) Viscosity Adjustment: Add an appropriate amount of solvent NMP to adjust the viscosity of the second slurry (each addition is made at a mass ratio of NMP:LMFP = 0.025 until the slurry viscosity is controlled within the range of 5000–7000 mPa·s). Control the stirring speed at 6.8 m / s, the viscosity adjustment time at 30 min, the temperature at 25 ± 2℃, and the vacuum degree at ≤-90 kPa. Adjust the slurry viscosity to 7000 mPa·s. After defoaming, pass the slurry through a 150-mesh sieve to obtain the lithium manganese iron phosphate cathode slurry. The mass ratio of LMFP, conductive carbon black, carbon nanotubes, PVDF, and dispersant in the prepared lithium manganese iron phosphate cathode slurry is 96.3:0.55:0.25:2.5:0.4.

[0085] In Comparative Example 2, the mass ratio of LMFP, conductive carbon black, carbon nanotubes, PVDF and dispersant in the lithium manganese iron phosphate cathode slurry was 96.3:0.55:0.25:2.5:0.4.

[0086] Step (7) Coating and Rolling: The lithium manganese iron phosphate positive electrode slurry obtained in step (6) is coated on carbon-coated aluminum foil with a single-sided density of 17.53 mg / cm2, a coating speed of 8 m / min, and a coating temperature of 84-93℃. After rolling, the electrode compaction density is 2.3 g / m3. After slitting, the LMFP positive electrode sheet is obtained.

[0087] The LMFP positive electrode sheet prepared above was used as the positive electrode of the lithium-ion battery, and the lithium-ion battery was prepared according to step (8) of Example 1.

[0088] Comparative Example 3 The lithium manganese iron phosphate cathode slurry, cathode sheet and lithium-ion battery were prepared according to the method of Example 1, with the only difference being in step (2) and step (5).

[0089] In step (2), carbon nanotube slurry (Cabot GNC-N-19) and binder solution are added to a mixing tank at a mass ratio of 1:6.3. The mixture is dispersed for 60 minutes under the conditions of a stirring linear speed of 13.4 m / s, a temperature of 35~45℃ and a vacuum degree of ≤-90kPa to prepare conductive agent solution A (different from the conductive agent solution in Example 1).

[0090] In step (5), the conductive agent solution A prepared in step (2) is added to the first slurry prepared in step (4). The mass ratio of LMFP in the first slurry to PVDF and carbon nanotubes in the conductive agent solution A added in step (5) is 96.3:2.5:0.25. The solvent NMP is added and pre-dispersed for 20 min under the conditions of stirring linear speed of 6.8 m / s, temperature control of 30~40℃, and vacuum degree of ≤-90kPa. Then, the dispersant is added. At this time, the mass ratio of LMFP to dispersant is 96.3:0.4. The slurry is dispersed at high speed for 120 min under the conditions of stirring linear speed of 17.7 m / s, temperature control of 30~40℃, and vacuum degree of ≤-90kPa. A second slurry with a viscosity between 5000 and 12000 mPa·s and exhibiting a fluid dynamic is prepared.

[0091] In Comparative Example 3, the mass ratio of LMFP, conductive carbon black, carbon nanotubes, PVDF and dispersant in the lithium manganese iron phosphate cathode slurry was 96.3:0.55:0.25:2.5:0.4.

[0092] The lithium-ion battery was prepared according to step (8) of Example 1.

[0093] Comparative Example 4 The preparation of lithium manganese iron phosphate cathode slurry, cathode sheet, and lithium-ion battery includes the following steps.

[0094] Step (1) Preparation of adhesive solution: Add PVDF adhesive and NMP solvent to a mixing tank at a mass ratio of 1:13.3, and pre-stir at a stirring speed of 2.7 m / s for 25±2℃ for 30 min (pre-stirring is to prevent PVDF from flying away and being drawn away during high-speed dispersion under vacuum, which would reduce the actual solid content); then disperse at a stirring speed of 18.7 m / s, a temperature controlled at 35~45℃, and a vacuum degree of ≤-90kPa for 150 min to prepare the adhesive solution.

[0095] Step (2) Activation mixing: The positive electrode active material LMFP and conductive carbon black (the mass ratio of LMFP to conductive carbon black is 96.3:0.55) are simultaneously added to the mixing tank for dry mixing. The linear velocity is controlled at 2.7m / s, the temperature is 25±2℃, and the stirring time is 30min to obtain the active powder.

[0096] Step (3) First addition of adhesive: The adhesive solution prepared in step 1 is added to the powder prepared in step 2. The mass ratio of LMFP in the powder to PVDF in the added adhesive solution is 96.3:1.25 (that is, the mass of PVDF added in step 3 accounts for 50% of the total mass of PVDF contained in the positive electrode slurry). Then, solvent NMP is added with a mass ratio of NMP:LMFP=0.22:1. The first slurry with a solid content of 72wt% is prepared by stirring at a linear speed of 0.5m / s, a temperature of 25±2℃ and a kneading time of 120min.

[0097] Step (4) Secondary Addition: Add the remaining adhesive solution prepared in Step 1 to the first slurry prepared in Step 3. At this time, the mass ratio of LMFP to PVDF in the adhesive solution is 96.3:2.5. Add solvent NMP, with a mass ratio of NMP:LMFP = 0.13:1. Pre-disperse for 20 min under the conditions of stirring linear speed of 6.8 m / s, temperature controlled at 30~40℃, and vacuum degree ≤-90kPa. Then add solvent NMP again, with a mass ratio of NMP:LMFP = 0.13:1, and stir linearly at 6.8 m / s. The mixture was pre-dispersed for 20 min at a temperature of 30-40℃ and a vacuum degree of ≤-90 kPa. Then, carbon nanotube slurry and dispersant were added. At this time, the mass ratio of LMFP to carbon nanotubes and dispersant was 96.3:0.25:0.4. The mixture was then dispersed at high speed for 120 min at a stirring linear speed of 17.7 m / s, a temperature of 30-40℃, and a vacuum degree of ≤-90 kPa to prepare a second slurry with a solid content of 58 wt%, a viscosity between 5000 and 12000 mPa·s, and exhibiting a fluid dynamic state.

[0098] Step (6) Viscosity Adjustment: Add an appropriate amount of NMP solvent to adjust the viscosity of the second slurry (each addition is made at a mass ratio of NMP:LMFP = 0.025 until the slurry viscosity is controlled within the range of 5000–7000 mPa·s). Control the stirring speed at 6.8 m / s, the adjustment time at 30 min, the temperature at 25 ± 2℃, and the vacuum degree at ≤-90 kPa. Adjust the slurry viscosity to 7000 mPa·s. After defoaming, pass the slurry through a 150-mesh sieve to obtain the lithium manganese iron phosphate cathode slurry. The mass ratio of LMFP, conductive carbon black, carbon nanotubes, PVDF, and dispersant in the prepared lithium manganese iron phosphate cathode slurry is 96.3:0.55:0.25:2.5:0.4.

[0099] Step (7) Coating and Rolling: The lithium manganese iron phosphate positive electrode slurry obtained in step (6) is coated on carbon-coated aluminum foil with a single-sided density of 17.53 mg / cm2, a coating speed of 8 m / min, and a coating temperature of 84-93℃. After rolling, the electrode compaction density is 2.3 g / m3. After slitting, the LMFP positive electrode sheet is obtained.

[0100] The LMFP positive electrode sheet prepared above was used as the positive electrode of the lithium-ion battery, and the lithium-ion battery was prepared according to step (8) of Example 1.

[0101] Comparative Example 5 The preparation of lithium manganese iron phosphate cathode slurry, cathode sheet, and lithium-ion battery according to the method of Example 1 includes the following steps: (1) Preparation of adhesive solution: Same as step (1) in Example 1.

[0102] (2) Preparation of conductive agent solution: Dispersant, conductive carbon black, carbon nanotube slurry and binder solution were added to a mixing tank at a mass ratio of 1:1.37:12.5:89.3. The mixture was dispersed for 80 min under the conditions of stirring linear speed of 13.4 m / s, temperature control of 35~45℃ and vacuum degree of ≤-90kPa to prepare conductive agent solution B (different from the conductive agent solution in Example 1).

[0103] (3) First addition of adhesive: The conductive agent solution prepared in step (2) is added to the LMFP powder, wherein the mass ratio of LMFP to PVDF, carbon nanotubes, conductive carbon black and dispersant in the conductive agent solution B added in step (3) is 96.3:1.25:0.125:0.275:0.2, that is, the mass of PVDF added in step (3) accounts for 50% of the total mass of PVDF contained in the positive electrode slurry, and the solvent NMP is added. The stirring linear speed is 0.5m / s and the kneading time is 120min to prepare the first slurry with a solid content of 72wt%.

[0104] (4) Secondary addition of adhesive: The conductive agent adhesive B prepared in step (2) is added to the first slurry prepared in step (3). The mass ratio of LMFP in the first slurry to PVDF, carbon nanotubes, conductive carbon black and dispersant in conductive agent adhesive B is 96.3:2.5:0.25:0.55:0.4. The solvent NMP is added and pre-dispersed for 20 min under the conditions of stirring linear speed of 6.8 m / s, temperature control of 30~40℃ and vacuum degree of ≤-90kPa. Then, it is dispersed at high speed for 120 min under the conditions of stirring linear speed of 17.7 m / s, temperature control of 30~40℃ and vacuum degree of ≤-90kPa to prepare a second slurry with a viscosity between 5000 and 12000 mPa·s and exhibiting a fluid dynamic state.

[0105] (5) Adjusting viscosity: Same as step (6) in Example 1.

[0106] (6) Coating roller pressing: Same as step (7) in Example 1.

[0107] (7) Preparation of lithium-ion batteries: Same as step (8) in Example 1.

[0108] In Comparative Example 5, the mass ratio of LMFP, conductive carbon black, carbon nanotubes, PVDF and dispersant in the lithium manganese iron phosphate cathode slurry was 96.3:0.55:0.25:2.5:0.4.

[0109] Comparative Example 6 The lithium manganese iron phosphate cathode slurry, cathode sheet, and lithium-ion battery were prepared according to the method of Example 1, with the difference being the following steps.

[0110] In step (2), the mass ratio of PVDF, carbon nanotubes and dispersant in conductive agent solution C (different from the conductive agent solution in Example 1) is 2.1:0.25:0.4.

[0111] In step (3), the mass ratio of LMFP to conductive carbon black is 96.7:0.55.

[0112] In step (4), the mass ratio of LMFP and conductive carbon black in the powder to PVDF, carbon nanotubes and dispersant in the conductive agent solution added in step (4) is 96.7:0.55:1.05:0.125:0.2, that is, the mass of PVDF added in step (3) accounts for 50% of the total mass of PVDF contained in the positive electrode slurry, and a first slurry with a solid content of 72wt% is obtained.

[0113] In step (5), the remaining conductive agent solution is mixed evenly with the first slurry, and the remaining steps are the same as in Example 1.

[0114] In Comparative Example 6, the mass ratio of LMFP, conductive carbon black, carbon nanotubes, PVDF and dispersant in the lithium manganese iron phosphate cathode slurry was 96.7:0.55:0.25:2.1:0.4.

[0115] Test case The fineness, solid content, viscosity, and viscosity change over 24 hours of the lithium manganese iron phosphate cathode slurry prepared in the examples and comparative examples; the appearance, interface condition, and folding state of the cathode sheet after coating; and the film resistance, peel strength, appearance, interface condition, and folding state of the cathode sheet after roll pressing are shown in Table 1 and 2. Figure 1 As shown in ~8.

[0116] The solid content of the positive electrode slurry was tested using a constant temperature bath. (1) Open the instrument cover, adjust the instrument level bubble to be in the center of the circle, confirm that the weighing pan is free of dirt and damage, turn on the power, enter the main interface, click the “GHL” option on the screen, enter the solid content measurement interface, set the test parameters to the drying temperature of 150℃, and turn off the standard 1mg / 90s; place the cut foil pad in the sample pan, close the cover and click the “O / T” key to peel.

[0117] (2) Take 3±0.3g of positive electrode slurry and spread it evenly on the pad paper. Close the top cover and click "Start Drying" to test.

[0118] (3) After the test is completed, the instrument will automatically display the test results.

[0119] The fineness of the positive electrode slurry was tested using a scraper fineness gauge. (1) Place the clean and dry fineness plate on a flat, level, non-slip flat experimental table.

[0120] (2) Use a glass rod to dip a small amount of the mixed positive electrode slurry above the maximum graduation line of the fineness plate. The amount of slurry should be slightly more than enough to fill the groove. Note that the sample should not contain air during the sampling and pouring process.

[0121] (3) Use your thumbs, index fingers and middle fingers to place the scraper horizontally on the upper part of the scraper, so that the edge of the scraper is in vertical contact with the surface of the scraper. Pull it from the deep part of the groove to the shallow part, and immediately observe the scale line where the particles in the groove are evenly exposed within 5 seconds. This value is the fineness of the sample.

[0122] (4) Immediately after the test, carefully clean the fineness plate and scraper with alcohol.

[0123] (5) Test results: The sample was measured in three parallel tests and the average value was taken.

[0124] The viscosity of the positive electrode slurry was tested using a viscometer. (1) Ensure the instrument is placed horizontally and use the built-in digital level to adjust it to a balanced state (avoid tilting which may affect accuracy). Turn on the instrument and warm it up for at least 20 minutes to ensure the internal temperature is stable. Select the appropriate L4 rotor and fix it with the magnetic coupler to ensure that the rotor is firmly connected to the host. Enable the Toolmaster™ function.

[0125] (2) Take 500ml of the freshly prepared positive electrode slurry from the mixing tank, adjust the lifting rod to make the rotor groove completely submerged in the slurry liquid surface, set the parameters to a rotation speed of 30rpm and a test duration of 4min, and click "Start" to perform the viscosity test.

[0126] (3) After the test is completed, the instrument will automatically display the test results.

[0127] The static viscosity of the positive electrode slurry was tested using a viscometer. (1) Ensure the instrument is placed horizontally and use the built-in digital level to adjust it to a balanced state (avoid tilting which may affect accuracy). Turn on the instrument and warm it up for at least 20 minutes to ensure the internal temperature is stable. Select the appropriate L4 rotor and fix it with the magnetic coupler to ensure that the rotor is firmly connected to the host. Enable the Toolmaster™ function.

[0128] (2) Take 500ml of the prepared positive electrode slurry from the mixing tank, let it stand for several hours and test the viscosity of the standing slurry. Do not stir the slurry before the test. Adjust the lifting rod to make the rotor groove completely submerged in the slurry liquid surface. Set the parameters to 30rpm and 4min for the test duration. Click "Start" to perform the viscosity test.

[0129] (3) After the test is completed, the instrument will automatically display the test results.

[0130] The diaphragm resistance was tested using a diaphragm resistance tester. (1) Turn on the computer, turn on the instrument power, start the instrument, click on the program interface, set the parameters to 20MPa and the pressure holding time to 2s.

[0131] (2) Lay the test sample (positive electrode) flat on the measuring platform, click test, and wait for the test to complete.

[0132] (3) Test results: Five parallel measurements were performed on the sample, and the average value was taken.

[0133] The peel strength test was conducted using a tensile testing machine. (1) Cut the positive electrode sheet to be tested into a test sample with a width of 30 mm and a length of 250 mm.

[0134] (2) Apply 3M double-sided tape to the test plate, roll it three times in the same direction with a pressure roller, peel off the tape, so that the sample and the adhesive are completely bonded, and then roll it three times in the same direction with a pressure roller to complete the sample preparation.

[0135] (3) Fix the test plate and the sample on the clamp of the tensile testing machine respectively, set the parameters: deformation value > 80mm, tensile speed 50mm / min, click start test, do not touch the sample during the test, and wait for the test to be completed.

[0136] (4) Test results: The A and B sides of the sample were tested in parallel, and the average value was taken.

[0137] Table 1: Performance Test Results of Lithium Manganese Iron Phosphate Cathode Slurry

[0138] Figure 6-1 The kneading results for Example 1 show that the kneaded slurry has no dry powder, good viscosity, and good kneading effect.

[0139] Figure 6-2 For comparison example 6, the kneading results showed that the material agglomerated, had no stickiness, and did not string, indicating poor kneading effect. This suggests that the amount of PVDF was insufficient, resulting in poor adhesion.

[0140] Figure 7-1 The coating of Example 1 shows that the coated film has the characteristics of a smooth and even surface, uniform coating, good adhesion, no material peeling, no scratches, and no bubbles.

[0141] Figure 7-2 Compared to the coating of Comparative Example 1, there were obvious raised particles, powdering, particle scratches, and film cracking.

[0142] Figure 7-3 For comparison example 5, the coating surface has slightly raised particles, but no particle scratches or powder shedding.

[0143] Figure 8-1 The example shows the folding of the roller-pressed electrode sheet in Example 1. No powder falls off when folded, and no foil leaks from the fold.

[0144] Figure 8-2 For comparison, the electrode sheet of roller pressing is folded in half. Folding it in half causes powder to fall off, and the creases are severe and the foil leaks out.

[0145] Figure 8-3 As a comparative example, the electrode sheet of the 4-roller pressing is folded in half. Slight powder loss and foil leakage due to folding are observed.

[0146] As shown in Table 1 and the attached figures, compared with Comparative Example 1 (dry homogenization process), Comparative Example 2 (one-time sizing process), and Comparative Example 3 (dispersant added later), Example 1 has the smallest slurry fineness and is more stable. It exhibits the best electrode peel strength, membrane resistance, electrode dispersion, and coating state, and the rolled electrode has good flexibility. Furthermore, the wet two-step sizing process significantly improves the dispersion of LMFP and small-particle-size conductive agents, and also demonstrates a significant effect in reducing viscosity and increasing solids content in the slurry.

[0147] The pure dry process used in Comparative Example 1 had a poor dispersion effect on LMFP, with the largest changes in slurry viscosity and solid content. Due to the poor dispersion effect, the corresponding electrode coating slurry either did not form a film or had an extremely poor coating condition.

[0148] In Comparative Example 2, the mixed adhesive was added all at once. This resulted in a large amount of high-strength adhesive tightly coating the small-particle conductive carbon black and nano-sized LMFP during the kneading process, easily causing agglomeration between them and preventing them from functioning effectively as kneaders. In addition, LMFP and small-particle conductive agents also absorbed a large amount of adhesive during the kneading process, easily causing the slurry to rebound significantly and become unstable. Therefore, the fineness of the slurry scraper and the coating condition of the electrode were slightly worse. During the thick coating process, the electrode was prone to cracking and material loss, and the rolled electrode was brittle after rolling, with severe cracks when folded.

[0149] In Comparative Example 3, although other homogenization processes were the same as in Example 1, the electrostatic repulsion and steric hindrance effects caused by the addition of dispersant limited the agglomeration of nano-sized LMFP and small-particle-size conductive carbon black in the slurry with higher viscosity after high-speed dispersion. This required extending the high-speed dispersion time, which was not conducive to controlling production costs. In order to meet the required discharge viscosity, more solvent NMP was required for viscosity adjustment. Therefore, its overall solid content was 1-2% lower than that of Example 1, and the slurry stability was worse. As a result, the dispersion state and electrode coating state of the slurry were poor, and the rolled electrode had micro-cracks when folded.

[0150] In Comparative Example 4, because the carbon nanotube slurry contains some NMP and additives, it is necessary to extend the high-speed dispersion time to achieve sufficient homogenization, resulting in low production efficiency. Furthermore, its dispersibility deteriorates in high-solids slurry, leading to local agglomeration of carbon nanotubes, uneven coating, severe agglomeration, and poor coating consistency. Therefore, the dispersion state of the slurry and the coating state of the electrode are slightly worse, and the rolled electrode has bright spots, micro-cracks when folded, and low peel strength.

[0151] In Comparative Example 5, the addition of SP to the adhesive with high bonding strength caused severe agglomeration of small-particle conductive carbon black, which could not be uniformly coated on the surface of nano-sized LMFP to form a conductive network. It also consumed the binder and easily caused the slurry to rebound significantly and become unstable. As a result, the viscosity stability of the slurry was poor and the coating state of the electrode was poor. During the thick coating process, the electrode had obvious protruding particles, and the rolled electrode was brittle, had bright spots, low peel strength, and cracks when folded.

[0152] In Comparative Example 6, due to insufficient binder in the slurry, the bonding force between conductive carbon black and small-particle-size, high-specific-surface-area LMFP is weak, making it easy for separation and agglomeration to occur. This leads to the agglomeration of nano-LMFP particles, resulting in slurry gelation and sedimentation.

[0153] Example 2 is similar to Example 1 in process, except that the amount of adhesive added at one time in Example 1 is smaller. This results in better kneading of LMFP and conductive agent in the less viscous slurry, thus improving the slurry dispersion and coating condition, and allowing for better folding of the rolled electrode sheet. It is evident that the appropriate batch addition and proportion of adhesive have a crucial impact on the dispersion of nano-sized LMFP and small-particle-size conductive agent.

[0154] In summary, by adding the adhesive solution of the prepared binder in two steps in the appropriate proportions in Examples 1 and 2, and uniformly dispersing the small-particle-size, high-specific-surface-area LMFP material, the resulting LMFP slurry has a higher solids content, smaller fineness, and greater stability than other methods. Under thicker coatings, it does not crack or scratch, exhibits better electrode flexibility, and shows significant improvements in peel strength and membrane resistance.

[0155] Any numerical value mentioned in this invention, if there is only a two-unit interval between any minimum and any maximum value, includes all values ​​that increase by one unit each time from the minimum to the maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, or time, is stated as 50-90, in this specification it means specifically listing values ​​such as 51-89, 52-88... and 69-71 and 70-71. For non-integer values, it may be appropriately considered that a unit is 0.1, 0.01, 0.001, or 0.0001. These are merely some specifically specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0156] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words and embodiments used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing lithium manganese iron phosphate cathode slurry, characterized in that, A conductive adhesive liquid is prepared, wherein the conductive adhesive liquid contains a binder, a dispersant, carbon nanotubes and a solvent, wherein the binder is polyvinylidene fluoride; The conductive agent solution is divided into two parts, P1 and P2; P1 is mixed with the active material to obtain the first slurry; P2 is mixed with the first slurry to obtain the positive electrode slurry. The amount of adhesive in P1 is M1, and the amount of adhesive in P2 is M2. By mass percentage, M1 / (M1+M2) = 40%~80%. The active material contains lithium manganese iron phosphate and conductive carbon black.

2. The method for preparing lithium manganese iron phosphate cathode slurry according to claim 1, characterized in that, Based on 100wt% of the active material, the amount of lithium manganese iron phosphate is 95wt% to 98wt%, the amount of conductive carbon black is 0.4wt% to 1wt%; and / or, the solid content of the first slurry is 65wt% to 75wt%. And / or, the adhesive accounts for 5% to 8% of the solvent by mass.

3. The method for preparing lithium manganese iron phosphate cathode slurry according to claim 1 or 2, characterized in that, Based on the amount of the conductive agent adhesive solution being 100wt%, the amount of the binder is 1.8wt% to 2.8wt%, the amount of the dispersant is 0.2wt% to 0.6wt%, and the amount of carbon nanotubes is 0.2wt% to 1wt%.

4. The method for preparing lithium manganese iron phosphate cathode slurry according to any one of claims 1-3, characterized in that, The solvent is N-methylpyrrolidone; And / or, the adhesive is one or more of HSV900, 5130, and 6020; And / or, the carbon nanotubes are one or more of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes; And / or, the dispersant is one or more of polyvinylpyrrolidone, sodium dodecyl sulfate, fatty alcohol polyoxyethylene ether, Tween-60, and dispersant KD-1.

5. The method for preparing lithium manganese iron phosphate cathode slurry according to any one of claims 1-4, characterized in that, The method further includes a post-processing step, which includes viscosity adjustment, defoaming, and sieving. Among them, when the viscosity of the positive electrode slurry is 5000-7000 mPa•s, defoaming and sieving are performed; When the viscosity of the positive electrode slurry is >7000 mPa•s, solvent is added to adjust the viscosity to 5000-7000 mPa•s before defoaming and sieving.

6. The lithium manganese iron phosphate cathode slurry prepared by the method according to any one of claims 1-5.

7. The lithium iron phosphate cathode slurry according to claim 6, characterized in that, The positive electrode slurry contains solid components, including lithium manganese iron phosphate, conductive carbon black, carbon nanotubes, binder, and dispersant, with mass fractions of 95%–98%, 0.4%–1%, 0.2%–1%, 1.8%–2.8%, and 0.2%–0.6%, respectively. And / or, the viscosity of the lithium manganese iron phosphate cathode slurry is 5000-7000 mPa•s; And / or, the fineness of the lithium manganese iron phosphate cathode slurry is 3-30 μm; And / or, the solid content of the lithium manganese iron phosphate cathode slurry is 50wt% to 65wt%.

8. A lithium iron phosphate positive electrode sheet, characterized in that, The slurry contains lithium manganese iron phosphate cathode material prepared by the method according to any one of claims 1-5, or contains lithium manganese iron phosphate cathode material according to claim 6 or 7.

9. The method for preparing the lithium manganese iron phosphate positive electrode sheet according to claim 8, characterized in that, The lithium manganese iron phosphate cathode slurry is coated on carbon-coated aluminum foil, with a single-sided density of 17~23 mg / cm³. 2 The coating speed is 5–10 m / s, the coating temperature is 84–93℃, and the compaction density is 2.0–2.5 g / cm³. 3 After being rolled and slit, lithium manganese iron phosphate positive electrode sheets are obtained.

10. A lithium-ion battery, characterized in that, The lithium-ion battery comprises the lithium manganese iron phosphate positive electrode sheet as described in claim 8.

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